The major goal is to investigate the critical factors that determine the specific functional characteristics of neuron populations. The two most likely variables that may be involved are (1) geometry of excitatory and inhibitory connections between units and (2) the specific metabolic properties of individual neurons within the population. The main problem under study is to determine the factors that control the development and modification of connections between units in excitable systems. We will complete the development of an insect central nervous system preparation where the 3-dimensional geometry of the dendritic tree of an adult motor neuron is quantitatively defined and the anatomy and physiology of 1 to 4 presynaptic fibers terminating on this post unit is determined. We will use the intracellular cobalt staining method developed in our laboratory and computer analysis of dendritic geometry for the structural identification. Then we will examine the following: changes in the form of the dendritic tree during degeneration and regeneration of the defined presynaptic input; observations on the development of the dendritic branching pattern including possible changes during metamorphosis; we will also place the cell bodies of identified neuron in tissue culture and attempt to induce sprouting from these cells to determine what factors control the branching pattern of dendrites. We will use our recently discovered phenomenon; that the drug colchicine greatly increases the electrical excitability of insect central nerve cell bodies; to investigate the relationship between electrical activity and macromolecular synthesis in neurons.